The present invention relates to fuel assemblies for nuclear reactors, for example of the ordinary water-cooled PWR type in which the actual fuel in the form of a large number of unit rods is grouped into autonomous bundles, each constituting a fuel assembly. As is known, such an assembly has an upper and a lower end plate interconnected by hollow guide tubes, which can particularly serve for the introduction of control rods or measuring devices. To these different guide tubes are generally fixed spacing grids which can sometimes freely slide about said guide tubes and in which are fixed the unit fuel rods by means of a spring system.
In known manner, the end plates are made from stainless steel and the guide tubes are made from zircalloy alloy which is permeable to the flux of neutrons traversing them.
As it is impossible to weld zircalloy to stainless steel, hitherto the guide tubes have been fixed to the stainless steel end plates by means of force fitting systems having undulations for preventing the longitudinal sliding of the tube in its support. However, such systems have a very poor resistance to the differential expansions between the different connecting members when the reactor temperature rises. Almost invariably, these expansions lead to both diametral and longitudinal deformations, so that at the end of a relatively short operating period the connection quality is impaired.